Revealing mistake: Jackie is shot in the head, and not only does his head not burst, but the snow mount in front is already covered all over in blood before he falls.
Visible crew/equipment: When AJ tries on his new military school uniform, he's pressured to also put on the hat. Then, after AJ looks at himself in the mirror, just as he walks back toward his mother, the reflection of the boom mic becomes visible in that mirror directly over Carmela's reflection, at the right side of the screen.
Answer: I'm not sure which person you're referring to here specifically, but the meaning is someone who makes a habit of constantly going to funeral calling hours (normally 2pm-5pm and 7pm to 9pm) for morbid entertainment or gossip purposes (elderly ladies, for example).
Ryan Grubb